I think, if we had a sustained (let's say 10 year) spell in the Premier League, then about 40k would probably be our ceiling in terms of regular gates. That's assuming we're a mid-to-lower-table side, and don't suddenly get fantasy land investment and "do a Newcastle."
A new Kop would be nice, but it would be ludicrously expensive. Knocking down the existing stand and clearing/prepping the ground would cost a fortune itself. I'm sure I've read somewhere in the past that there is the risk of UXB's from the Blitz in the huge earth pile that it sits on, which if true would only add to the expense (needing military staff to sweep and clear the area). That might be an urban myth, but it wouldn't suprise me if true. Only then could we start on the expense of constructing a whole new stand.
I know fuck all about football ground architecture, but I can't imagine there'd be much change out of £15m or so to build a modern, well-equipped stand with the same or slightly larger capacity as the current kop.
As long as we're yoyoing, it doesn't make financial sense to outlay that much cash. I sit/stand on the kop, and I'd love to have a nice, modern, covered concourse, but not at the expense of investment in the playing squad, the training facilities, or calling in a hit on the Shirecliffe Sniper.
